A gas turbine engine combustion chamber assembly comprises combustion chamber including a head at its upstream end which has one or more apertures and a corresponding fuel injector is arranged in each of the apertures. A fuel injector generally comprises a fuel injector head having one or more coaxially arranged air swirlers. Currently the majority of fuel injectors are rich burn fuel injectors, but lean burn fuel injectors are desired to reduce emissions from gas turbine engine combustion chambers.
Rich burn fuel injectors generally comprise a fuel injector head which comprises a first air swirler, a first pre-filming surface arranged around the first air swirler and a second air swirler arranged around the first-pre-filming surface and a third air swirler arranged around the second air swirler. Lean burn fuel injectors generally comprise a fuel injector head which comprises a first air swirler, a first pre-filming surface arranged around the first air swirler, a second air swirler arranged around the first-pre-filming surface, a third air swirler around the second air swirler, a second pre-filing surface arranged around the third air swirler and a fourth air swirler arranged around the second pre-filming surface. In some lean burn fuel injectors the fuel injector head also comprises an additional air swirler between the second air swirler and the third air swirler.
Lean burn fuel injector heads require a greater number of air swirlers and this increases the diameter of the fuel injector heads and hence increases the diameter of the apertures in the head of the combustion chamber and the diameter of the apertures in a combustion chamber casing surrounding the combustion chamber.
In one arrangement of combustion chamber assembly each aperture in the head of the combustion chamber has an associated air swirler and the corresponding fuel injector head comprises at least one air swirler and the fuel injector is positioned coaxially within the air swirler in the aperture. In this arrangement there is a problem of relative movement between the fuel injector head and the head of the combustion chamber during operation. This relative movement may lead to misalignment between the air swirler within the aperture in the head of the combustion chamber and the fuel injector head. This may be detrimental to the aerodynamics of the air flows from the fuel injector and the air swirler, may lead to incorrect mixing of the fuel and air and hence incorrect combustion within the combustion chamber, affecting the emissions from the combustion chamber and the acoustic response of the combustion chamber.
In another arrangement of combustion chamber assembly each aperture in the head of the combustion chamber does not have an associated air swirler and the corresponding fuel injector head comprises at least two coaxially arranged air swirlers and the fuel injector head is positioned within the aperture. In this arrangement the aperture in the head of the combustion chamber has a larger diameter to accommodate the fuel injector head comprising at least two coaxially arranged air swirlers. The larger diameter of the aperture in the head of the combustion chamber may increase the stresses within the head of the combustion chamber and may result in cracking. In addition an aperture in a boss of a surrounding combustion chamber casing has a larger diameter to enable the fuel injector to be inserted through the combustion chamber casing to the combustion chamber head. The boss of the combustion chamber casing has to be stronger to support the fuel injector and this adds weight to the combustion chamber casing. The larger diameter of the aperture in the combustion chamber casing may increase the stresses within the combustion chamber casing and may result in cracking. The fuel injector is more expensive due to the manufacturing cost of providing an additional coaxial air swirler on the fuel injector head.
Therefore the present invention seeks to provide a novel combustion chamber assembly which reduces, or overcomes, the above mentioned problems.